1. Field of the Invention
This invention relates to methods of dispersing carbon nanotubes in solutions. More specifically, the invention is a method of aqueous solution dispersement of carbon nanotubes.
2. Description of the Related Art
Carbon nanotubes (CNTs) possess superior mechanical and electrical properties thereby making them a potential material of choice for a wide variety of applications. However, CNTs are not readily dispersed in a solvent because of substantial van der Waals attraction between CNTs. Unfortunately, dispersion of CNTs into individual tubes or small bundles of tubes in often desirable when another material is to be bonded to the CNTs. That is, if the CNTs can be dispersed prior to having a material bonded thereto, the resulting material tends to exhibit homogenous properties.
The choice of dispersing solvent must be compatible with the CNTs, the material being bonded thereto, and possibly the ultimate application environment. Ideally, the dispersing solvent is a water-based or aqueous system owing to water's low cost, ready availability, and non-toxic nature. Use of an aqueous dispersing solution is especially desirable in biomedical or biophysical applications. However, the hydrophobic nature of CNTs has made it difficult to disperse CNTs in an aqueous system.
To combat the CNTs aversion to dispersion in an aqueous system, surfactants or amphiphilic polymers are typically added to the aqueous system. Exemplary surfactants or polymers include sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (NADDBS), TRITON X-100, TWEEN 20, PLURONIC P103, dodecyltrimethylammonium bromide (DTAB), DNA and polystyrene)-poly-(ethylene oxide) (Ps-PEO) diblock copolymer. CNT dispersion is stabilized as the surfactants wrap around the CNTs.
For dispersions requiring a high concentration of CNTs (i.e., higher than 0.1 mg/ml), the surfactant concentration required usually exceeds critical micelle concentrations to prevent re-aggregation of the CNTs after dispersion. However, most surfactants are not biocompatible and are difficult to remove from final products due to their strong adsorption onto the CUT surfaces. Also, surfactants hinder binding of reactants onto CNTs due to their tight wrapping of CNT surfaces. A low-power and high frequency sonicator is often utilized to make the suspension of CNTs with conventional surfactants. However, this process takes a long time (e.g., normally sonication for over 24 hours is required using this approach) to make a well-dispersed CNT suspension.